Slope Protection Effect Contrastive Studies on Soil Bioengineering Measures for Natural Stream Bank and Artificial Slope

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1 2011 International Conference on Asia Agriculture and Animal IPCBEE vol.13 (2011) (2011)IACSIT Press, Singapoore Slope Protection Effect Contrastive Studies on Soil Bioengineering Measures for Natural Stream Bank and Artificial Slope Wang Ying, Gao Jiarong+, Gu Lan, Qian Bintian Key Laboratory of Soil and Water Conservation and Desertification Combating of the Ministry of Education,Beijing Forestry University, ,Beijing China Abstract. Soil bioengineering is a kind of slope ecological restoration technology which is very vigorous. It is the use of living plant materials just like root, stem and branch or even the whole to perform specific engineering functions in the process of plant growth and phytocommunity construction for the purpose of slope stabilization, water and soil conservation and river ecosystem improvement. Researches based on the experiments settled in natural stream bank of Liuli River and artificial slope of Changping by using Salix alba var. tristis and Salix matsudana materials have been compared in the respect of soil bioengineering restoration application in this paper. The result indicates that: repairing effects in artificial slope is better than in natural stream bank. The figure of infant root growth vigor shows: After 5-month project implementation, significant effectiveness was obtained on slope stability, the new biomass of Salix alba var. tristis applied in artificial slope is 28.7% bigger than that in natural stream bank; The new biomass of Salix matsudana applied in artificial slope is 36.4% bigger than that in natural stream bank. The figure of root maximum tensile test also shows: Salix alba var. tristis applied in artificial slope is 1.4 times bigger than that in natural stream bank; Salix matsudana applied in artificial slope is 1.3 times bigger than that in natural river bank. Keywords: Soil bioengineering, Salix alba var. tristis, Salix matsudana, slope protection 1. Introduction Soil bioengineering is a kind of biological technology based on reliable soil engineering. It is a kind of integrated engineering technology which can stabilize the steep slope, reduce water and soil erosion and improve the environment by constructing variety side slopes (Mountain slope, river bank and coast slope) which is under the use of plants and other auxiliary materials [1~4]. The use of natural materials such as plants and soil in slope protection can date back to the ancient time of China. Soil bioengineering has been brought to Europe since the 16th century. In the latest 30 years, a lot of research has been done and great progress has been made on this sphere. It has been widely used to stabilize the slope surface in Europe. Recently, scholars in China come to do some research on soil bioengineering. Experimental area such as a 4- km-long river way located on shanghai Pudong international aerodrome, has been put to use to prove the superiority of soil bioengineering. This project aims to find the development potential of soil bioengineering in China. Jiarong Gao [5~8] has been making use of bio-engineering measures to repair the river ecology in Beijing, which can offer technical guidance and theory basement to river ecological restoration in Beijing even the nation as a whole. Salix alba var. tristis and Salix matsudana have been selected to do this research. To conduct an ecological restoration experiment in Liuli River, it needs to investigate and monitor the growth condition of plants, and evaluate the suitability. This paper is based on contrastive studies about the soil shear, habitat condition and biodiversity between natural stream bank and artificial slope before and after the soil bioengineering implement. Studies and demonstrate projects indicate that using the soil bioengineering measures can stabilize the slope bank, improve the habitat suitability and restore the Gao Jia-rong. Tel.: address: jiaronggao@sohu.com 192

2 environment. Soil bioengineering [9 ~ 13] could be widely applied in ecological restoration of all kinds of slopes in China Research area profiles Application of soil biological engineering is studied in Changping and Huairou District, including artificial slope in Changping District and ecological remediation at Liuli River in Huairou. Changping is located at northwest Beijing, which has longitude scope E ~ ,N ~ ", and belongs to Semihumid Temperate District. This is profoundly manifested in the following ways: high-cool rich-wind arid climate in the spring, hot and rainy in the summer, cool autumn and cold and dry in winter. Average of annual sunshine hours, temperature and annual rainfall is respectively about 2684h, 11.8 and mm. Annual sunshine hours is between 2748h and 2873h.The frost-free period is about d.Average temperature is from6 to 12. Annual rainfall is about mm. The average of annual sunshine hours, temperature and annual rainfall in huairou district is respectively about 2748h, 10.5 and 645.0mm. A 40m long and 45 gradient soil slope was artificially built in White floating village in Changping in April, Five measures (including live stake, live pole drains, brush, live silt fences, live gully breaks) have been governed to artificial slope with experimental material such as Salix matsudana, Salix Alba var. tristis, Amorpha fruticosa L. and so on. In addition, a soil biological engineering construction was carried in 150 meters long river reach of Liuli River in May in The demonstration figure in experimental area is as follows: Fig.1 Experiment site of measures allocation in Liuli River Fig.2 Experiment site of measures allocation in Changping 1.2. Construction methods Live Stake Live stake is one of the soil bioengineering measures. After certain processed, plants live branches which are likely to survive, according to certain angle, are directly inserted into the soil. In this study, we choose Salix alba var. tristis and Salix matsudana branches with diameter for 1-3cm around, length for about 30-50cm. The best right size of diameter is 3cm, and the best right size of length is 40cm. These branches are inserted into the soil according to a certain angle of 45 degrees, with scissors repair after inserting. Distance between branch and branch is about 1m or so. The first column and second column branches are interlaced. These branches can also be inserted into the rocks and the cage made with lead wire. After plants live, the roots, soil and rock will fix together. What s more, the lead wire on the cage will fall off over for a long period of time, Then the roots of the plants can be able to replace the fixed function of the cage. Clearance between the roots can provide shelter space for marine life. Live staking is a simple, economic and fast measure. The only fly in the ointment is that plants could not play a role to protect the slope immediately after the completion is used to restore slopes by constructing a fill-slope consisting of alternating layers of live branches and soil, creating a series of reinforced benches. In some cases, fill materials must be placed on steep (1.5:1 or greater) angles due to the geometry of the site. In these cases (2 to 5m long) can be inserted 193

3 into the fills as they are constructed. The branches provide immediate protection against surface erosion. It involves the cutting and placement of live branch cuttings on slopes. The live cuttings eventually root and provide permanent reinforcement. When local overstepping of the fill is required, for example where gullies cross slopes that are being deactivated, development of brush layers in fills may be particularly useful. This will provide stability to the fill and will eventually result in the development of shrubby vegetation along the gully. Scheduling requirements for the use of cuttings may dictate that machine work be organized for these sites during seasons when cuttings can be used Investigation and monitoring One month after the completion, monitor and survey is very important. Various indicators such as plant survival rate, coverage, the base diameter and new branch height should be valued. In order to make a better assessment, slope reinforcement effect of plants in ecological improvement action should be investigated five months later (in the first plant growth season). Then make comparisons adaptability of plants between artificial slope and natural stream banks. 2. Analysis of Results 2.1. The growth characteristics of slope-protecting plants Under the measure of live stake From Table 1, under the use of live staking measure on artificial slope, the average base diameter of Salix alba var. tristis s fresh branches reaches 8.0mm; average height is 115.6cm. The average base diameter of Salix matsudana's fresh branches reaches 6.4mm, average height up to cm. On natural stream bank, the average base diameter of Salix Alba var. tristis s fresh branches reaches 6.4mm, average height is 57.2cm. The average base diameter of Salix matsudana s fresh branches reaches 6.2mm, average height up to 99.5mm. The survival Salix Alba var. tristis and Salix matsudana have achieved a high level of growth condition under the implement of different soil bioengineering technologies Under the measure of brush Under the use of brush measure on artificial slope, the average base diameter of Salix Alba var. tristis s fresh branches reaches 5.4 mm; average height is 92.0 cm. The average base diameter of Salix matsudana 's fresh branches reaches 6.4 mm, average height up to cm. On natural stream bank, the average base diameter of Salix Alba var. tristis s fresh branches reaches 3.6mm, average height is 52.3cm. The average base diameter of Salix matsudana 's fresh branches reaches 4.9mm, average height up to 76.8mm. 1 (p<0.01) Table 1 Growth of plants under different soil bioengineering measures on different types Type artificial slope natural stream bank Cuttings (Single) Salix alba var. tristis Salix matsudana Salix alba var. tristis Salix matsudana Completed five months Planting New diameter New length technique (mm) (cm) Live strakes 8.0±0.5a 115.6±6.9a 5.4± ±5.5 Live strakes 6.2±0.4c 99.5±8.4d 6.4± ±5.8 Live strakes 6.4±0.3b 57.2±43.0b 3.6± ±44.3 Live strakes 5.0±0.2bc 71.7±20.3d 4.9± ±6.7 The results show that the germination rate and the survival rate of Salix alba var. tristis and Salix matsudana is all more than 90% since several of soil biological engineering measures have been constructed for five months. It shows that Salix alba var. tristis and Salix matsudana are adaptability to the northern part of China. From Table 1 we can get the following conclusion: the application of living staking measure leads 194

4 to result that the average basal diameter and height of Salix alba var. tristis of natural slope are respectively 20.0% and 50.5% smaller than that of artificial slope.the same goes for Salix matsudana, which figure is separately19.4% and 27.9%. While under the measure of brush, the average basal diameter and height of Salix alba var. tristis in natural slope is respectively 33.3% and 43.2% smaller than that of Salix alba var. tristis in artificial slope. And the data goes to 16.7% and 22.1% for Salix matsudana by the same measure. Analysis of variance shows that there is significant difference (p < 0.01) between Salix alba var. tristis grown on natural stream bank and Salix alba var. tristis planted on artificial slope Soil biological engineering in slope protection effect Slope protection effect of soil bioengineering plant roots is essential to slope stability. The shear or bond strength is always proportionate to the roots biomass. The biomass of neonatal roots and branches of the two kinds of plants which are planted on artificial and natural stream banks is shown in Table 2. After fivemonth s growth, the underground root depth of Salix alba var. tristis and Salix matsudana can reach 1m. The biomass of neonatal roots of the two plants planted on artificial slope is 4.02g/4.78g respectively, while the biomass of neonatal branches is 22.86g/36.55g and the average of max root tensile force is N/802.92N. For the situation of these two plants planted on natural stream bank, the corresponding data are 2.87g/3.04g, 16.57g/22.45g, and N/663.93N. Table 2 Comparison of New root biomass and root maximum tensile strength on different types Type Species of cuttings New root biomass (g) New biomass (g) root tensile strength (N) maximum Number of cutting artificial slope natural stream bank Salix alba var. tristis ± Salix matsudana ± Salix alba var. tristis ± Salix matsudana ± From Table 2, for the plant of Salix alba var. tristis, the root biomass of natural stream bank is 28.7% smaller than that of artificial slope; the maximum root tensile strength of artificial slope is 1.4 times bigger than that of natural stream bank. For the plant of Salix matsudana, the root biomass of natural stream bank is 36.4% smaller than that of artificial slope; the maximum root tensile strength of artificial slope is 1.3 times bigger than that of natural stream bank. 3. Conclusion and Discussion The experiment about soil bio-engineering on natural stream bank of Liuli River and Changping artificial slope shows that this technology is very viable in the use of ecological restoration. By using viable plant roots, stems (branches), or the overall structure, soil bio-engineering technology can stabilize the bank slope and prevent water loss and soil erosion by means of plant construction. The above discussion indicates that soil bio-engineering applied to artificial slope is better than the natural stream bank. All this can be manifested in the following: After 5-month project implementation, significant effectiveness has been obtained on slope stability, habitat improvement and ecological restoration. It was concluded that the approach could be widely applied in slope ecological restoration in China. Under the measure of living staking, the average DBH and diameter of Salix alba var. tristis on natural slope is separately 50.5% and 20.0% smaller compared with that planted on artificial slope; the average DBH and diameter of Salix matsudana on natural stream bank is separately 27.9% and 19.4% smaller compared with that planted on artificial slope. Similarly, under the measure of brush layer, the average DBH and diameter of Salix alba var. tristis on natural slope is separately 33.3% and 43.2% smaller compared with that planted on artificial slope; the average DBH and diameter of 195

5 Salix matsudana on natural stream bank is separately 16.7% and 22.1% smaller compared with Salix matsudana planted on artificial slope. In artificial slope, the newly born biomass allocation of Salix alba var. tristis root is 28.7 %bigger than that in natural stream bank. The same, Salix matsudana applied in artificial slope is 36.4 % bigger than that in natural stream bank. The figure of root maximum tensile test also shows: Salix alba var. tristis applied in artificial slope is 1.4 times bigger than that in natural stream bank; Salix matsudana applied in artificial slope is 1.3 times bigger than that in natural stream bank. Further research is required on other factors which are related to the ecological restoration effect of soil bio-engineering such as construction time, cover hickness and the choice of plant species. The adaptation of plants in practical application is the core and foundation technique of Soil bio-engineering. The research we have done can be served as reference in the future ecological restoration in Beijing district. More research about shear and tensile strength, characteristics of plant growth is the main development trend. 4. Acknowledgment This Research is supported by the International Scientific and Technology Cooperation Program of MOST China (2009DFA32490). The authors would like to thank all members of Key Laboratory of Soil and Water Conservation and Desertification Combating of the Ministry of Education the for discussion. 5. References [1] Gao Jiarong, Wang Fang. Discussion on soil bioengineering in riparian zone in Miyun Reservoir watershed [J]. Research of Soil and Water Conservation2006, 13(3): [2] Li Xiaoping, Zhang Liquan. Application and effectiveness of soil bioengineering in ecological restoration of stream bank [J]. Chinese Journal of Applied Ecology :2005, 24(1): 7-12 [3] Gao Jia-rong, Liu Ying Hanspeter Rauch. Application Experiment of Soil Bioengineering in River Ecological Restoration in Beijing [J]. Journal of Soil and Water Conservation: 2008, 22(3): [4] ZHOU Yue. Vegetation and erosion control: exploration on basic principle of slope engineering [J]. Journal of Soil and Water Conservation: 2000, 11 (2): [5] LOU Hui-pin; GAO Jia-rong; Liu Ying; Lv Jing; Wang Ying. Application of Soil Bioengineering on Road Slope Revegetation in Beijing Suburb[J]. Journal of Northwest Forestry University: 2010,25(6)64~68 [6] Liu Ying; GAO Jia-rong; Zhang Jin-rui; Lv Jing. Construction and application of cutting and riprap joint planting technology [J]. Advances in Science and Technology of Water Resources: 2009, 29(4): [7] Liu Ying; Wang Fang; GAO Jia-rong. Root Distribution Characters of Ostryopsis davidiana on Different Sites in the Loess Plateau of Western Shanxi. Journal of Northwest Forestry University: 2009, 24(1): [8] Shields, Jr., F. D., S. S. Knight, and J. M. Stofleth Stream bed organic carbon and bioticintegrity. Aquatic Conservation: Marine and Freshwater Ecosystems 18(5): [9] Shields, Jr., F. D., N. Morin, and C. M. Cooper Large woody debris structures for sand-bed channels. Journal of Hydraulic Engineering 130(3): [10] France R L.Biomass and production of amphipods in low alkalinity lakes affected by acid precipitation [J]. Environmental Pollution, 1995, 94(2):189~193. [11] Li M H, Karen E.E. Biotechnical engineering as an alternative to traditional engineering methods, a biotechnical stream bank stabilization design approach [J]. Landscape and Urban Planning, 2002, 60:225~242. [12] Athol D A, Lin G. Step pool stream: adjustment to maximum floe resistance [J]. Water Resource Research, 1995, 31(10):2593~2602. [13] Gregory S V, Lambert G A, Moore K M S. Influence of valley floor landform s on steam ecosystems [M], USDA Forest Serbice Gen, Tech, Rep